JPS58113362A - Production of hot dipped steel plate with zinc - Google Patents

Abstract

PURPOSE:To produce a hot dipped steel plate with zinc which is alloyed on one side at a low cost by machining the surface on one side of the steel plate to a fresh surface in the stage before the passage of the steel plate through a zinc bath is completed and applying plating on said surface then wiping the same. CONSTITUTION:In the stage before the passage of a steel plate through a zinc bath is completed in a plating pot 1, the surface on one side of the steel plate is machined with a metallic brush roll 2 or the like to a fresh surface and plating is applied on said surface. After the plating, the excess molten zinc stuck on the fresh surface is removed by gas wiping 3. If the surface of the steel plate is refreshed, the alloying speed of the zinc film is markedly improved, and the alloying of said surface is effected only by the heat capacity that the steel plate possesses after the wiping and no influence is given at all upon the non- alloyed surface. It is preferable in terms of acceleration of alloying and advantageousness in workability to make the coating weight of the molten zinc on the fresh surface of the steel plate smaller than the coating weight on the other surface by the wiping after the plating.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a hot-dip galvanized steel sheet (hereinafter referred to as GI/GA steel sheet) whose negative side is alloyed and the other side remains galvanized.

Hot-dip galvanized steel sheets and so-called alloyed hot-dip galvanized steel sheets (hereinafter simply referred to as alloyed steel sheets), which are alloyed with this galvanized film, have a wide range of uses as relatively inexpensive anti-corrosion materials. ing.

However, each of these has advantages and disadvantages, and in reality, these alone cannot sufficiently meet the needs of users. Alloyed steel sheets have significant advantages over regular hot-dip galvanized steel sheets in terms of paintability and weldability, but on the other hand, the coating is fragile, so it is difficult to thin the coating for processing purposes. Therefore, a sufficient anticorrosion function cannot be expected. On that point, regular hot-dip galvanized steel sheets have good properties in terms of workability, especially in terms of compressive deformation, so even when used for processing purposes, it is possible to ensure high corrosion protection through thick plating. be.

However, this originally has major disadvantages in terms of paintability and weldability.As a result, recent efforts have been made to achieve both advantages by using GI/Gl, which is alloyed only on the negative side. A board was created. In other words, this means that one side (alloyed surface) is painted, but the other side (lead plated side) is left unpainted and used as an excellent anti-corrosion surface. It has a wide range of uses. However, this G.I./
There is still no satisfactory method for manufacturing GA steel sheets. The most commonly considered
This is a method in which the injection pressure of a gas knife after hot-dip plating is increased on the side of the steel plate to be alloyed to reduce the amount of plating deposited on that surface as much as possible, and then alloying is performed. In other words, a difference is created in the amount of plating deposited on both sides of the steel plate, and this difference is used during the alloying process to achieve alloying on only one side. However, the formation of a considerable amount of alloy phase is unavoidable, and therefore the original workability of the non-alloyed film cannot be guaranteed.

One possible solution to this problem is to cool the non-alloyed surface during heating in the alloying process to prevent it from being heated. However, in general, the thermal conductivity of metals is extremely low, and it is true that it is nearly impossible to keep one side of a steel plate in a cooled state while the other side is kept in a heated state, as described above, but this is possible. Even if this were the case, the thermal loss during its implementation would be expected to be enormous.

The present invention makes it possible to stably produce a GI/GAfili plate in which both the alloyed and non-alloyed surfaces have their original properties, and to reduce the production cost and efficiency to the conventional method of producing galvanized steel sheets. The purpose is to provide a method for manufacturing GI/GA steel sheets that is comparable in comparison.

In other words, the gist of the present invention is that when manufacturing a hot-dip lead-plated steel sheet, one surface of the steel sheet is mechanically processed to form a new surface and plated before the steel sheet completes passing through the zinc bath. A method for producing a GI/GA steel sheet, characterized in that excessive molten lead on the surface of the steel sheet is removed by wiping, and only the newly formed surface is alloyed.

Based on the method of the present invention, the surface to be alloyed of a steel plate is made into a new surface by mechanical processing before passing through the zinc bath, and when the waste lead melt adhering to this new surface is removed by wiping after plating, the wiping If is sufficient, alloying of the surface will be achieved. In other words, by forming a new surface, the alloying speed of the zinc film on the surface is dramatically improved, and as a result, it becomes possible to achieve alloying on the surface using only the heat capacity of the steel strip after wiping. be. In this case, in the method of the present invention, the above-mentioned mechanical processing is not performed on the non-alloyed surface.
No such alloying occurs. In addition, if the wiping ability is insufficient and alloying of the newly formed surface cannot be completed by wiping alone, alloying of the surface can be reliably achieved by further heat treatment at a temperature of 280°C or higher. be. In this case, it is preferable to increase the N concentration in the zinc bath, specifically to 0.15% or more, to prevent the progress of alloying on the non-alloyed surface due to heat treatment. That is, the addition of N to the zinc bath has the effect of suppressing the diffusion of the Fe--Zn alloy layer of the zinc coating.

The effect of providing a new surface based on the method of the present invention is hardly affected by this N, and therefore, even if the N concentration is increased as described above, it does not seem to have an adverse effect on the alloying behavior of the alloyed surface. There are no concerns at all.

In the case of the method of the present invention, regardless of whether or not the above-mentioned alloying heat treatment is performed, when removing fusible lead from the steel sheet surface by wiping, the basis weight of the newly formed surface is smaller than that of the non-alloyed surface. It is preferable to do this because "the thicker the basis weight of the alloyed surface is, the disadvantageous it is to processing, and the smaller the amount of date on the surface, the faster the alloying will be completed, and the more reliable the alloying of the non-alloyed surface. This is because it can be prevented.

In addition, even if alloying by wiping is not completely completed, if only a thin η phase remains on the surface layer, it is possible to perform only surface grinding of the η phase on the alloyed surface without performing the above heat treatment. .

Mechanical processing in the method of the present invention refers to anything generally referred to as surface machining, such as polishing, grinding, blasting, and metal brushing using various devices. Basically, this mechanical processing may be carried out at any time before the passage of the zinc bath is completed, regardless of the type of line. However, if the steel plate is heat treated in-line,
In the so-called Sendzimir method or non-oxidation furnace method, it is most effective to carry out the process after the heat treatment has been completed.

When implementing a flux method that assumes out-of-line annealing, there is no significant difference in effectiveness at any stage before the completion of passing through the zinc bath. Mechanical processing is performed at one location or at multiple locations at such stages.

A sufficient alloying rate cannot be expected unless the temperature of the alloying treatment, which is carried out as necessary, is at least 280''C.

When carrying out alloying treatment, it is preferable to keep the N concentration in the zinc bath at 0.15% or higher, as mentioned above, but this is at most i, ost, and if it exceeds this, the surface quality of the non-alloyed surface will deteriorate. is damaged.

Next, the effects of implementing the present invention will be explained.

[Example 1] A 50-fi wide steel strip (SPCG) was continuously annealed at 750'C in an atmosphere of 10 N2 (30% by weight of H2), cooled to 420°C, and then exposed to a zinc bath for 2 seconds. Plating was carried out by the Sendzimir method of immersion in the liquid. At this time, as shown in FIG. 1, a metal brush roll (2) was installed in the plating pot (1), and mechanical processing was performed only on one side in the plating bath. Plating bath temperature 460°C1
The N concentration in the bath was maintained at 0.22%. After plating, only on the mechanically processed side (alloyed side) - the amount of zinc deposited was reduced to 60 f/m1'' by gas wiping (3).

Regarding the sample taken from the obtained plated steel plate, 370
Double-sided heating was performed in a 'C box furnace. Still for comparison,
Amount of lead deposited on zinc-plated steel sheet under the same conditions as above except that machining using the brush roll (2) was not performed:
14! M/n? (non-alloyed surface) '60 f/hexametal alloyed surface) was obtained, and this was also subjected to the above-mentioned double-sided heating.

The ratio of the amount of alloy layer to the amount of film-like butt plug film was investigated by anodic constant current electrolysis when the heat treatment time was varied. The results are shown in Table 1. In the figure, ◯ indicates that the film characteristics of each surface are satisfactory, and × indicates that the film characteristics are also unsatisfactory.

In Table 1-L, as shown in the comparative example, when the conventional method was used, the non-alloyed surface had also been alloyed for more than h by the time the alloying of the alloyed surface was completed, which was compared to the conventional method. It can be seen that good workability of the alloyed surface cannot be obtained using this method. Furthermore, the time required to complete metallurgy using conventional methods is extremely long. In contrast, in the example of the present invention, alloying was obtained only on the mechanically processed surface (alloyed surface) by heat treatment for a relatively short time.

[Example 2] Pre-ground steel plate (5PCC) on one side (QJ3+m thickness
5Qm width x 150cm length) was plated using the fluff method by dipping it in a zinc bath with a N concentration of 0.17% for 5 seconds, and then wiping gas was injected only on one side of the steel plate (the mechanically processed side). , 1102/rr? (Surface without mechanical processing) 155r/n? (machined surface) plated steel plate was created.

At the same time, a plated steel plate was produced under the same conditions as above, except that the as-cold-rolled base material was used.

These plated steel plates were heated at 550°C until alloying on the thinner side was completed; however, the required furnace time for alloying was 2 minutes for the ground material that had been machined in advance; It took 10 minutes for the non-grinded material using the base material.

Furthermore, FIG. 2 shows the results of anodic constant current electrolysis during the heating process described above. In the same figure, B1 is the ground treated material, and the non-alloyed surface of the non-grinded material is the basis weight side], B2
Similarly, these are the results for each alloyed surface (light weight side). From the comparison between B1 and B1, it is clear that the properties of the non-alloyed surface are improved by employing the method of the present invention.

As explained above, the method of the present invention is a GI/
GAM plates can be manufactured in a short period of time, and the implementation cost is not much different from conventional methods. Therefore, the present invention can be said to have extremely high practical value.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a plating apparatus used for implementing the method of the present invention, and FIG. 2 is a graph showing the effects of implementing the present invention. In the diagram: 1 = Metsuki pot, 2: Metal brush roll, 3: Gas wiping. Applicant: Sumitomo Metal Industries, Ltd.

Claims (1)

[Claims] (1) When manufacturing hot-dipped curved lead-plated steel sheets, one side of the steel sheet surface is mechanically processed to form a new surface before the steel sheet completes passing through the lead bath, and after plating, wiping is performed to clean the steel sheet surface. A method for manufacturing hot-dip galvanized steel sheets characterized by removing excess molten zinc and alloying only the newly formed surface 0 (2) By wiping after plating, the basis weight of molten zinc on the newly formed surface of the steel sheet is reduced to the basis weight of other surfaces of the steel sheet. 2. The method for producing a hot-dip galvanized steel sheet according to claim 1, wherein the amount is less than the amount.